Multiple light paths architecture and obscuration methods for signal and perfusion index optimization
A photoplethysmographic (PPG) device is disclosed. The PPG device can include one or more light emitters and one or more light sensors to generate the multiple light paths for measuring a PPG signal and perfusion indices of a user. The multiple light paths between each pair of light emitters and light detectors can include different separation distances to generate both an accurate PPG signal and a perfusion index value to accommodate a variety of users and usage conditions. In some examples, the multiple light paths can include the same separation distances for noise cancellation due to artifacts resulting from, for example, tilt and/or pull of the device, a user's hair, a user's skin pigmentation, and/or motion. The PPG device can further include one or more lenses and/or reflectors to increase the signal strength and/or and to obscure the optical components and associated wiring from being visible to a user's eye.
1. A wearable electronic device comprising:
a first window, a second window, a third window and a fourth window;
an optical isolation separating each of the first, second, third and fourth windows;
a first light sensor positioned behind the first window;
a second light sensor positioned behind the second window;
a first light emitter that emits first light, the first light emitter positioned behind and off-center with respect to the third window, the first light emitter located a first separation distance from the first light sensor and a second separation distance from the second light sensor, wherein the first separation distance is less than the second separation distance;
a second light emitter that emits second light, the second light emitter positioned behind and off-center with respect to the fourth window, the second light emitter located a third separation distance from the second light sensor and a fourth separation distance from the first light sensor, wherein the third separation distance is less than the fourth separation distance; and
a first lens located between the first light emitter and the third window; wherein:
the first light sensor detects at least one of the first light and the second light and generates first signals indicative of physiological information of a user;
the second light sensor detects at least one of the first light and the second light and generates second signals indicative of physiological information of the user; and
the first lens is configured to direct the first light around the optical isolation.
2. The wearable electronic device of claim 1 , wherein:
the first light sensor is centered within the first window; and
the second light sensor is centered within the second window.
3. The wearable electronic device of claim 1 , wherein the first lens further comprises a Fresnel lens, an image displacement film or a brightness enhancement film.
4. The wearable electronic device of claim 1 ,
wherein the optical isolation is further positioned between the first light sensor and the first light emitter.
5. The wearable electronic device of claim 1 , wherein the third separation distance is less than the first separation distance.
6. The wearable electronic device of claim 1 , wherein the second separation distance is less than the fourth separation distance.
7. The wearable electronic device of claim 1 , further comprising:
a second lens located between the first light sensor and the second window.
8. The wearable electronic device of claim 7 , wherein the second lens is configured to shift light onto an optical receiving area of the first light sensor.
9. The wearable electronic device of claim 8 , wherein the first lens comprises a Fresnel lens, an image displacement film or a brightness enhancement film.
10. A method of determining physiological information of a user, the method comprising:
at a device having:
a first window and a first light sensor positioned behind the first window,
a second window and a second light sensor positioned behind the second window;
a third window and a first light emitter positioned behind the third window and that emits a first light;
a fourth window and a second light emitter positioned behind the fourth window;
an optical isolation separating each of the first, second, third and fourth windows; and
a first lens located between the first light emitter and the third window and configured to direct the first light around the optical isolation:
emitting the first light from the first light emitter, the first light emitter positioned off-center within the first window;
receiving a first portion of the emitted first light by the first light sensor, the first light sensor located a first separation distance from the first light emitter;
receiving a second portion of the emitted first light by the second light sensor, the second light sensor located a second separation distance from the first light emitter, wherein the first separation distance is less than the second separation distance;
emitting second light from the second light emitter, the second light emitter positioned off-center within the second window;
receiving a first portion of the emitted second light by the second light sensor, the second light sensor located a third separation distance from the second light emitter;
receiving a second portion of the emitted second light by the first light sensor, the first light sensor located a fourth separation distance from the first light emitter, wherein the third separation distance is less than the fourth separation distance; and
determining the physiological information using the received first portion of the emitted first light and the received first portion of the emitted second light.
11. The method of claim 10 , wherein the physiological information includes perfusion index information, the method further comprising:
determining the perfusion index information using the received second portion of the emitted first light and the received second portion of the emitted second light.
12. The method of claim 11 , further comprising:
removing noise from the physiological information using the perfusion index information.
13. The method of claim 10 , further comprising:
generating first signals from the received first portion of the emitted first light and the received first portion of the emitted second light;
generating second signals from the received second portion of the emitted first light and the received second portion of the emitted second light; and
selecting between the first signals and the second signals based on the user's skin type.
14. The method of claim 10 , further comprising:
generating first signals from the received first portion of the emitted first light and the received first portion of the emitted second light;
generating second signals from the received second portion of the emitted first light and the received second portion of the emitted second light; and
selecting between the first signals and the second signals based on a usage condition.
15. The method of claim 10 , further comprising:
changing a first angle of the first light emitted from the first light emitter to a second angle, wherein the second angle is greater than the first angle relative to normal incidence.
16. The method of claim 10 , further comprising:
changing a third angle of light received by a device to a fourth angle, wherein the fourth angle is less than the third angle relative to normal incidence.
17. The method of claim 10 , further comprising:
collimating the first light emitted from the first light emitter using a second lens located between the first light emitter and the first window.